The present invention relates generally to detecting a condition in the environment. Particularly, the invention pertains to apparatus and methods to detect the presence of carbon monoxide and smoke in the atmosphere.
The threat of carbon monoxide poisoning has increased dramatically in the past decade. Carbon monoxide is a colorless, odorless, tasteless gas, making it virtually impossible to detect its presence. Carbon monoxide can be produced by various fuel burning appliances, such as, fuel fired furnaces, gas hot water heaters, gas stoves, gas dryers, space heaters, charcoal grills, fireplaces, vehicles, lawn mowers, or snow blowers. Once present, this gas circulates freely throughout a building, such as a home. If this gas is not ventilated properly, carbon monoxide poisoning may result.
Carbon monoxide inhibits the blood""s ability to carry oxygen to body tissue, including vital organs such as the heart and brain. When carbon monoxide is inhaled, it combines with oxygen-carrying hemoglobin of the blood to form carboxyhemoglobin. Once combined with the hemoglobin, the hemoglobin is no longer available for transporting oxygen. The amount of carboxyhemoglobin that builds up is a factor of the concentration of the gas being inhaled and the duration of the exposure.
Carbon monoxide can act in the body in high concentrations, or slowly over a long period of time. Because it takes several hours to remove carbon monoxide from the body of a person, concentrations of carbon monoxide can gradually build up in the blood causing headaches, fatigue, dizziness, nausea, burning eyes, or unconsciousness.
Devices for sensing carbon monoxide and triggering an alarm in the presence of excess concentrations of carbon monoxide are presently available. These CO detectors typically employ a solid state sensor which purges itself and resamples for carbon monoxide on a periodic basis. However, conventional carbon monoxide detectors usually do not account for low levels of the carbon monoxide gas over long periods of time. Known detectors of this type are intended to be plunged into AC receptacles and are not battery powered.
Other types of known CO detectors utilize biomimetic sensors. Such devices are battery powered and detect changes in opacity of the biomimetic material.
In addition to being generated by operation of various products, carbon monoxide is produced along with smoke by fire. Fire detectors operate on different principles than do carbon monoxide detectors. Known fire detectors respond to heat, flame or smoke.
The range of presently available products includes separate carbon monoxide and fire detectors. It would be useful if the sensing characteristics of these separate units could be incorporated into a single, easy to use, easily installed, multi-mode product.
In view of the above, the present invention provides methods and apparatus for monitoring the presence and changes in the concentration of carbon monoxide. A detector that embodies the invention may also detect the presence of smoke.
In one aspect, a combined smoke and CO detector is battery operated. The detector carries a carbon monoxide sensor that is sealed until it is to be used by a consumer.
The CO sensor is carried within a housing and is not user replaceable. Removable tape seals the CO sensor until the detector is put into service. The sealing tape is applied when the carbon monoxide sensor is assembled. When a user places the detector into service the tape is removed thereby exposing the CO sensor to the ambient air.
An ionization-type smoke sensor is also carried within the housing. Both sensors are coupled to a programmed processor. The detector is energized by a single replaceable battery.
The process, in response to signals from the sensors, can produce an audible alarm indicative of the presence of carbon monoxide. A different audible alarm, for example in accordance with NFPA standard No. 72, can be produced to indicate the presence of smoke. In one aspect, if both carbon monoxide and smoke are present, the processor can go immediately unto a fire alarm indicating state.
In yet another aspect, a test circuit can be provided. For example, activating the test button can test each sensor sequentially. In this instance, appropriate audible alarms can be alternately produced.
In one aspect, a smoke determination can be made independently of a CO determination The smoke determination can predominate and force the generation of visible and audible alarms.
Visual indicators of an alarm condition provide visual feedback to users. In one aspect, a symbol indicates if smoke is present and can be illuminated in the presence of detected levels thereof. Similarly, in the presence of pre-selected levels of carbon monoxide, a visual symbol indicative thereof can be illuminated. The visual indicators can be sequentially illuminated during a test sequence.
In yet another aspect, the detector and both of the sensors can be energized by a single battery. For example, a removable battery door can be provided. If the door is mounted in a user accessible side of the detector it will be possible to replace the battery with removing the detector from its mounted location.
The detector periodically measures the output of a CO sensor. The detector subtracts each sampled CO sensor output from the previous sampled sensor output. The difference of between the successive sampled sensor outputs are summed. The detector unit determines the rate of change of the sampled sensor outputs to determine the level of CO in the atmosphere. The detector can actuate an alarm when a predetermined CO condition is detected.
The methods and applications of the present invention provide a highly efficient and low cost detector that is capable of detecting the presence of carbon monoxide at an early stage to allow persons to evacuate the area. The detector can also detect low concentrations of carbon monoxide over long periods of time. The detector unit may also detect the presence of smoke.
The invention, together with further attendant advantages, will best be understood by reference to the following detailed description of the presently preferred embodiments of the invention, taken in conjunction with the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.